Pulverizing process and apparatus



Dec. 9, 1930. w. B. PEDELTY ,975.

PULVERIZING PROCESS AND APPARATUS Filed Feb. 27, 1929 Fly] ii iii.

A? n f INVENTOR.

TTORNEYJI Patented Dec. 9, 1930 UNITED STATES PA'rsNr oFFics I Warren a. rnnnrn, or mason crr'r, IOWA Application filed rem-nar 2%, ma. Serial no. a4a,ovs.

I v i I Tlns inventlon relates to nnprovements 1n pulverizing processes and apparatus of the' general type employed for feeding finely divided fuel to furnaces. 5 In apparatus of this general type it is common to mount upon a single s 1 breakers or grinders and a centrifugal fan for delivering the finely divided portions of material into the furnace. In the use of'such apparatus for feeding blast furnaces great difiiculties have been experienced by reason of the larger particles fallin'g to the bottom of the retort while only partially consumed and becoming mixed with molten metal to form a slag which is very difiicult to remove,

' blasting operations beingsometimes resorted to for that purpose. Y

To overcome this difficulty various expedient-s have been tried, one of the most commen being toprovide a wall or shoulder between the breaking or grinding portion of the apparatus and the fan in order to oh- 4 struct the passage of the largerfragments into the fan while allowing the smaller fragments to be thrown over such wall or shoulder. This expedient has proven effective'to 'aconsiderable extent inkeeping the larger fragments out of the fan but it has not prevented slag forming fragments from passing through the fan to the furnace. a

he primar object of my invention is to reduce pulverizable'materials b entraining such materials in an elastic fiu1 and churnin or impacting them against each other a eld or maelstrom of eddies induced by the operation ofa centrifugal fan at one side of said field, the materials or fragments of materials being caused to impinge upon each other throughout the field while moving frees ly and promiscuously in various directions.

My invention is distinguished from a pulverizing ap aratus in which materials and air are mec banically propelled and driven into contact with each other in sucha man- .ner as to produce crushing and abradingcon- 'ing apparatus embodying my inventlon.

tacts, and which propelling operation requires to be many times repeated in orderto reduce solid materials to the condition of a powder process, the material is preferably drawn aft a set of or a dust. In the practice of my into the pulverizing field by suction and after it has once enteredsuch field it isiheld in suspense without contact with moving mechanical driving mechanism until reduced-to the desired degree. of fineness determined by the carryin capacity of an outflowingor'centrifuga y dls'charging stream of air.

my invention to provide a fan which will effectively agitate small fragments of fuel and More particularly stated itis an object of 1 similar material or materials capable of bea ing entrained in air and pulverized by impact of one portion upon another within a fan casin and at one side of the fan wings as to cause them to break or pulverize each other so completely that the material may be dey livered from the fan casing substantially in the form of dust-and whereby solid fuels such as coal maybe so pulverized as to be substantially capable of suspension in the heated atmosphere of the furnace orretort until 3 invention rests upon the discovery'that a fan may be so constructed-that the major portion of the material will not'reach the space occupied by the wings until after it has been caught in one or more powerful eddies or conflicting air currents and thrown violently against other particles of the material with impacting'and grinding effects, whereby the material is almost instantaneously-reduced to a size havin' the characteristic of dust in that it is capab e of being held in suspension in the atmosphere fora considerable period of time. t

It may therefore be stated that it is an object of this invention to provide a process for utilizing violently agitating air to effect a finalpulverization of material and to deliver such material in an air stream wherein it is capable of floating until consumed-in a combustion chamber.

In the drawings: I

Figure 1 is a side elevation of a pulveriz- Fi-gure 2 is fa sectional view of the fan as taken on line 2-2 of Figure 1. t

Figure. 3 is a detail side view of the fan. Like parts are identified by the samereference characters throughout the several views.

In the practice of m process I first reduce the material to small ragments by an suitable means, these fragments being pre erably of such fineness that the can be entrained and carried in high ve ocity air streams. Thereupon I feed these fragments into a maelstrom of violently agitating air having a multitude of gyrating or cross currents of such intensity as to entrain the particles of material and throw them violently against each other and against any obstruction in their path. The velocity and'force of the air currents is proportioned to the force required for crushing the particles of material when .brought in contact with each other in the described manner.

My process also contemplates a continuous deliver of dust laden air from one side of the agitating field in which the fragments are bein crushed and a corresponding continuous delivery of fragments to be reduced into said field from another side.

My preferred means for practicing the process and for feeding the material into and out of the space within which the material is being reduced, will now be described more particularly with reference to the accompanying drawings.

In the drawings, a breaker 10 of ordinary construction is conventionally illustrated, from which fuel or other .material may be delivered through a'chute or assage 11 to an inlet opening 12 of a centri ugal fan casing 13. The breaker and the passage 11 may be of any ordinary construction, or any desired means may be substituted for initially reducing the material into comparatively small fragments such as have heretofore been delivered to furnaces.

The casing 13 is similar in form to the casings of centrifugal fans in common use, the inlet 12 being located at the so called eye or in the side wall of the casing opposite that at which the shaft 14 enters and the outlet passage or chute 15 being tangential in order that the fan wings may throw air and other material in the desired direction.

I have discovered that by mountin upon the shaft 14 a set of fan wings 17, pre erably two wings diametrically opposite and of a width approximately one half to nearly two thirds that of the casing, it is possible to set up gyrating currents and cross currents in the portion of the casing between the wings and the inlet side, and thereby throw the fragments of material violently against each other and against the peripheral wall portion 18 of the casing in such a manner as to ahnost instantly reduce said fragments to dust.

If the fragments enter the spaces between the wings 17 to any considerable extent I am unable to find any evidence of that fact.

The wing surfaces do not become polished and the encircling peripheral portion of the casing does not become polished, even after prolonged periods of use. It is evident that if any fragments enter the space between the wings they are immediately thrown laterally and caught in the swirls and cross currents at the side of the wings. Air and finely divided particles are, however, constantly delivered through the outlet chute. 15 in which no fragments of sufiicient size to be classed as other than dust have as yet been discovered, althoughrepeated tests have been made of the material passing through this chute.

The rapidity with which fragments of coal or similar material may be reduced to a dust indicates that the vortex or maelstrom developed in the open space between the inlet and the fan wings is composed largely of a multitude of eddies each revolving-about its own axis, whereas, all of these eddies also travel in a circular path about the central axis of the fan shaft extended. Also, there appears to be a pulsating movement due to the fact that, as the fan revolves, the air in the space which it occupies tends to become compressed in front. of the wings and a vacuum tends to develo in the rear of the win with the result t at the air in front of ti e wings is not only drivenoutwardly by centrifugal force, but develops a strong tendency to flow laterally into the space between the fan and that wall of the casing which is provided with the inlet, whereas, air and other material in such space tends to develo a counter-flow toward the rear side of eac wing. The air and other material entering through the inlet, is also necessarily flowing in a general direction perpendicular to the plane of the vortex, and the combined effect is to increase the random element to a point where collisions take place with almost inconceivable frequency.

It also appears probable that the multitude of cross currents, developed by-the pulsating effects of the fan wings and by the incoming material, operate to so diminish the general movement of revolution about the central axis as to prevent centrifugal force from developing in the vortex space to a degree sufficient to carry the larger fragments out of the vortex zone, and this appears to account for the fact that only dust laden air passes through the outlet chute.

In my improved fan I employ wings 17 having flat convergent surfaces, the wings being therefore wedge shaped, with the tips or outer margins substantially parallel to the shaft axis. Fan wings of this general type are disclosed in my former patent for a centrifugal fan dated September. 27, 1927 and numbered 1,463,317 but for the purpose of my present invention I'prefer to construct these wings of cast steel, suitably cored to a reduce their weight. I

P fact that but two diametrically opposite wings are employed, are material factors in developin the necessary agitation inthe air between t e inlet and the wings. However this may be, as compared with results obtainable from some of the other types of fans, it is certain that in a large art the results above described are obtained y reducing the width of the wings so as to allow a considerable s ace between them and the inlet side of the an casing. I have found that with wings constructed as above described I ob-.

' tain the best results by mounting the wings ,on the shaft in close proximity to the closed wall of the casing and (provide space between them and the inlet si width more than half that of the wings.

3 Such a fan delivers the fuel dust in a, pulsating current of high frequency, and these pulsations are also an effective aid to combustion in that they tend to break up circulation streams of the gases in the com,- bustion chamber. 4

By employing a two wing fan having a diameter of about twenty two inches from the tip of one wing to the tip of the other" with blades about eight inches in width, a

casing inlet about sixteen inches in diameter, and an'outlet about twelve inches square,

- with approximately four and one-half inches between the inlet side of the casing and the fan wings, and by revolving such a fanat approximately 2000 R. P. M., I am enabled to completely reduce the coal fragments to a dust and to deliver such dust to a burner in a pulsating current as above described, without causing the fanwingls to become abraded or even polished-and wit only a light polishing effect upon that portion of the casing which encircles the four and one-half inch space at one side ofthe fan wings.

I claim:

1. The process of pulverizing and feeding 1 fuel consisting in generating a zone of multiple eddies and cross currents having a general path of revolution about a common axis, feedm fragments of solid fuel into said zone a ong said common axis whereby the fragments are driven against each other to crush the same byimpacts 'and grinding contacts of such intensity as to reduce the fuel fragments to a dust, and delivering such dust, entrained in a portion of thee dying air, out of the space occupied by the eddies.

2. The process of pulverizing material consisting in generating a field of high velocity cross currents and eddies having a gen erally circular movement about a common axis and delivering fragments of pulveriz- .able material into such currents, to be carried by the currents of air into contact with each other to pulverize the same by impact parently the form of the wings and the e of the casing, of a,

- breaking the fuel into fra fan casing at the si tor-currents.

4. The process of pulverizing material, consisting in generating a r valving;eham-. ing maelstrom of such material and anelastic fluid within anunobstructed whorl shaped space, feeding elastic fluidfand material to 1 bepulverized' into said maelstrom at oneside .thereof, and delivering the pulverized material from 'saidina'lstrom tangentiallyfwhen the particles aresufliciently reduceddn size to becar'ried with portions of the elastic fluid out-of said maelstrom 'by centrifuga f 5. Apparatus, for pulverlzin'g f rising the {combination h casing having its inlet disposed to receive such fragments, and a centrifugal'fan' rotor occupying substantiall a half portion of the die opposite the inlet, said casing having a tangentially extending outlet passages. y v

6. Apparatu .for pulverizing fuel,-comprising the combination of means for breakmgthe fuel into fragments, of a fan casing having its inlet disposed to receive such fragments, and a centrifugal fan rotor occupying substantially ahalf portion of the fan casing at the side opposite the inlet, said casing having a tangentially extending outlet passage, and said fan rotor comprising a pair of oppositely extending flat surfaced wings.

7. The combinationof a fan having a sup porting shaft providedwith a pair of oppositely extending wings a casing for the wings of a width substantiall double the width of the wings and arranged with said wings and provided with a side inlet, said wings being located within the casing adjacent to the side opposite the inlet, and .means for feeding fuel through the inlet in fragments of a size to be lifted and thrown against each other inlet.

8. The combination with a coal breaker of the furnace fueling type, of a centrifugal fan having a casing provided with an inlet to receive coal from the breaker, and also having a tangential outlet for delivering the fuel to the combustion chamber of a furnace, said fan having its casing containing a set of fan win at the side opposite the inlet,

by the air between the fan wings and the and at a su stantial distance from the inleti whereby the fragments of fuel and the air entering through the inlet may be agitated to reducethe fragments to a dust before delivery by the fan wings through the tangential outlet.

9. Pulverizing apparatus comprising a centrifugal fan casing provided with an inlet aperture in one side wall and a drivipfi shaft extending through the other side w and provided with aset of fan win in close proximity to said last mention wall of materially less width thanthe width of the casing, the space between said wings and the wall provided with the inlet being open and unobstructed and of suflicient capacity to allow air and the material to be pulverized to be drawn by suction through said inlet and churned in said space by currents in duced by the revolving wings in such space.

10. Pulverizing apparatus comprising a centrifugal fan having a casing of materially greater width than the rotor, said rotor bemg located ad'acent one'side wall, and the opposing wall aving an inlet duct for feeding air and material to be pulverized into the space at the side of the rotor b suction induced by the rotoliiiand means or revolving said rotor at a su cient speed to develop a churning maelstrom in the space between it and the inlet, whereby the material may be reduced to a dust by impact and abrasion of the articles u 11 each other.

VFZLTER B. PEDELTY. 

